[flang] Implement C_F_STRPOINTER (Fortran 2023) (#176973)
Implement C_F_STRPOINTER to associate a Fortran character pointer with a
C string.
This intrinsic has two forms:
C_F_STRPOINTER(CSTRARRAY, FSTRPTR [,NCHARS]): Associates FSTRPTR with a
C string array
C_F_STRPOINTER(CSTRPTR, FSTRPTR, NCHARS): Associates FSTRPTR with a
C_PTR pointing to a character string
Implementation includes semantic validation, FIR lowering, and
associated tests.
F2023 Standard: 18.2.3.5
AI Usage Disclosure: AI tools (Claude Sonnet 4.5) were used to assist
with implementation of this feature and test code generation. I have
reviewed, modified, and tested all AI-generated code.
